Examples

Black can deliver x-ray mate with Rh1#.
The rook protects the pawn on h4, which is guarding the escape square on g3.

Black can deliver x-ray mate with Qd4#.
The queen protects the rook on b2, which guards the escape squares d2, c2, b3, and b4.

How to Spot X-Ray Mate

When the king attacks one of your pieces, your first thought is likely to move that piece to a safe square. But a check that protects the attacked piece can often be more powerful, because it keeps the attacked piece in the attack instead of retreating it — and it brings another piece into the attack as well. Checks that x-ray protect the piece can be easy to overlook.

Related patterns

In X-ray defence, an attacked piece is protected "through" the attacking piece.
X-ray mate is an x-ray defence and a checkmate at the same time.